This invention relates to electronic passive night vision aids and to a system for operating such night vision aids in conjunction with a local display such as a cockpit display. More particularly, the invention relates to an electronic night vision aid which amplifies light and may be used with a local display. A typical local display used with this invention is a head down display (HDD) used to provide instrumentation and other data to the viewer. It is intended that the local display may be viewed either with or without the night vision aid in use.
Passive night vision aids such as ambient night vision (ANVIS) goggles are becoming popular in the military aircraft cockpit setting. The increased popularity of such night vision goggles and other passive night vision aids creates unique problems with illumination of cockpit displays. These passive night vision aids operate by amplifying available light, particularly in the longer wavelengths of visible light. In the upper infrared ranges, illumination from cockpit display sources overwhelms sensor elements which are used in such night vision aids, and thereby interrupts the night vision aid for up to several minutes.
It is important that the display indicators remain illuminated, not only for the benefit of the crewmen who are not wearing night vision aids, but also because those using the goggles will typically view the instruments by looking under the goggles. In an attempt to alleviate this problem of cockpit displays overwhelming ANVIS devices, attempts have been made to filter the light from these display sources to restrict illumination to wavelengths not normally received by the night vision goggles. Filtration of the objectionable light must be very efficient because small amounts of light within the active frequency range of the night vision aid will overwhelm the aid. This becomes difficult due to the close proximity to the night vision aid of illuminated indicators.
Conventional passive night vision aids are sensitive to light having wavelengths of 580 nM or longer. This means that illumination of displays at shorter wavelengths (frequencies above the frequency range of the passive night vision aids) will not substantially interfere with the night vision aids and will facilitate the use of such night vision aids. The selective filtration of light according to wavelength generally prevents the use of full color displays. This is because frequencies at the lower end of the visible spectrum overlap with those frequencies which are received by the night vision goggles.
It is accordingly desired that a night vision aid such as ambient night vision (ANVIS) goggles be operable while a full color display is presented in the vicinity of the goggles. In particular, it is desired to operate ANVIS goggles in a cockpit or similar environment in which a full color display is illuminated. It is therefore desired to prevent light which originates at the full color display from overwhelming the night vision aid.